Switch-extender and a method for calibrating

ABSTRACT

A switch-extender is connected to a measurement system and to several DUTs. It splits a signal from the measurement system into several signals so that the several DUTs receive the same signal and can therefore be tested in parallel. The switch-extender further includes at least one amplifier and/or at least one attenuator for every output port so that every signal has the same signal level no matter what the individual attenuation factor of the signal connectors or of the internal printed circuit board is. Furthermore a method for calibrating the measurement system as well as for the switch-extender and the signal connectors describes how to obtain the needed calibration values both for the downlink path and for the uplink path without changing the signal connector.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of U.S. application Ser. No.13/657,419, filed Oct. 22, 2012, the content of which is incorporatedherein by reference in its entirety.

The present application claims foreign priority to European PatentApplication No. 12 158 439.5, filed on Mar. 7, 2012, and claims priorityto U.S. Provisional Application No. 61/569,352, filed on Dec. 12, 2011,the entire contents of which are herein incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a switch-extender and a method forcalibrating a measurement system with such a switch-extender, especiallyfor testing mobile communication systems, for example mobile phones,handhelds, tablet PCs and WLAN-routers.

Discussion of the Background

Due to the increasing number of mobile communication systems, forexample mobile phones, there is a strong demand in reducing the overalltest time. As the complexity of mobile communication systems increasesfrom generation to generation, the required test time also increases.Therefore, it is very difficult to reduce the test time for each mobilecommunication system. Therefore, the approach of the present inventionis that the overall test time can be reduced significantly by testingseveral mobile communication systems, like mobile phones, in parallel.

Document US 2005/0264373 A1 describes a switching matrix that allowsconnecting multiple input ports to multiple output ports as well as topower sources. It is disadvantageous that document US 2005/0264373 A1does not allow compensating different signal behavior in differentsignal path. Therefore, an input signal which is output at several portshas a different signal level which makes a switching matrix unsuitablefor supplying a plurality of mobile communication systems in parallelwith a test signal.

SUMMARY OF THE INVENTION

Therefore, embodiments of the present invention advantageously provide aswitch-extender and a respective calibration method that allowsconnecting one input port to several output ports at the same time andthat ensures that the signal level at every output port can be adjustedseparately.

The inventive switch-extender has at least one input port and severaloutput ports, wherein the at least one input port and the several outputports are connected to a first Multiplexer/Demultiplexer-means (in thefollowing MUX/DEMUX-means or -unit) wherein the first MUX/DEMUX-meansconnects the at least one input port to all output ports, wherein theMUX/DEMUX-means comprises at least one amplifier for amplifying a signalat the at least one input port and/or wherein the MUX/DEMUX-meanscomprises at least one attenuator for each of the output ports forattenuating a signal at every output port.

It is very advantageous that at least one amplifier is connected to theat least one input port and/or the at least one attenuator is connectedto each of the output ports. Therefore, a signal, which is split todifferent output-ports can be amplified to a certain signal level andthen attenuated by an individual attenuation factor (attenuation value)to compensate for the individual signal path to obtain output signalshaving a predetermined signal level. This allows that every DUT that isconnected with the switch-extender receives a test signal having exactthe predetermined signal level which makes the whole test proceduremeaningful and allows to compare the DUTs (devices under test) to eachother.

The inventive method is used for calibrating a measurement systemcomprising a measurement unit, a switch-extender connected to themeasurement unit and several signal connectors having one end connectedto the switch-extender and several attenuators connected to an other endof the several signal connectors and one calibration system wherein asequence of procedural steps are executed. First of all the other end ofone signal connector is connected with an attenuator to the calibrationsystem. Then a signal is generated with a specific signal level and/or aspecific signal frequency with the measurement unit. After that a signallevel and/or a signal frequency is measured with the calibration systemat the output of the attenuator. In the following a difference betweenthe measured signal level and/or the measured signal frequency and thegenerated signal with the specific signal level and/or the specificsignal frequency is determined. Finally calibration data are calculatedby using the determined difference between the measured signal leveland/or the measured signal frequency and the generated signal with thespecific signal level and/or the specific signal frequency.

It is advantageous that the signal connectors are used which are lateralso used for the measurement of the DUTs. This means that thedetermined difference and the calculated calibration data can be usedlater.

It is also advantageous if a second attenuator is connected in serieswith the at least one attenuator and if the at least one attenuator hasa larger attenuation range and higher attenuation steps than the secondattenuator. This allows that the at least one attenuator is used as acoarse attenuator having a wide attenuation range and that the secondattenuator can be used for a fine attenuation thereby allowing to adjustthe attenuation factor (attenuation value defining the attenuationlevel) over a wide range accurately.

It is further beneficial if a coupling-unit is connected between theleast one attenuator or the second attenuator and the correspondingoutput port and if the coupling-unit has a third port at which a signalis transmitted that is input in the corresponding output port. Thisallows that the output port can be used as bidirectional port for thereflected and/or transmitted signal which is input thereto as well.

It is also advantageous if at least one input port and several outputports are connected to a second MUX/DEMUX-unit wherein the secondMUX/DEMUX-unit comprises the same elements as the first MUX/DEMUX-unitwith the difference that the at least one input port is connected to aswitch and if one output port of the switch is connected to an inputport of an amplifier and if an other output port of the switch isconnected to an output port of another amplifier so that the at leastone input port acts as bidirectional port. This allows that the onlyinput port of the second MUX/DEMUX-unit that is connected to themeasurement unit can be used as a bidirectional port. A DUT connected tothe output port of the second MUX/DEMUX-unit can therefore transmit asignal to the second MUX/DEMUX-unit that will be forwarded to themeasurement unit.

However, another advantage exists if the switch-extender comprises aplurality of first MUX/DEMUX-units and a plurality of secondMUX/DEMUX-units wherein the input ports of the plurality of secondMUX/DEMUX-units are connected to an input port of a multiplexer, whereinthe output port of each multiplexer is connected to at least oneamplifier of each of the plurality of the second MUX/DEMUX-units andwherein the output ports of each multiplexer are connected to the outputof another amplifier of each of the plurality of the secondMUX/DEMUX-units. This allows that every second MUX/DEMUX-unit canmultiply the number of output ports addressable by the individualMUX/DEMUX-unit by the number of other MUX/DEMUX-units. Therefore, DUTshaving more antennas can be tested without difficulties.

Last but not least it is also very advantageous if the switch-extenderfurther comprises a processing unit and a storage unit connected to eachother wherein the processing unit controls the amplification settings ofthe at least one amplifier and wherein the processing unit also controlsthe attenuation settings of the at least one attenuator so that thesignal has at every output port a predetermined signal level for everyfrequency. This ensures that the switching times are reduced to aminimum, so that changes in the signal level resulting from changes inthe frequency of operation can be compensated fast.

It is also very advantageous that the method for calibrating ameasurement system includes the switch-extender that further comprisesat least one attenuator or at least one attenuator and a secondattenuator in series for every output port and that the attenuationfactor of the at least one attenuator is adjusted or that theattenuation factor of the at least one attenuator and the secondattenuator is adjusted, so that the measured signal level and/or signalfrequency of the signal is equal to the generated signal with thespecific signal level and/or the specific signal frequency. This ensuresthat despite one input signal being split into several output signals,every output signals has the same signal level.

BRIEF DESCRIPTION OF THE DRAWINGS

Different embodiments of the present invention are described exemplaryin the following in reference to the description. This is done by theway of example without limitation. The same subject matter has the samereference signs. The figures in the drawings show in detail:

FIG. 1 a measurement system, a switch-extender and several DUTsaccording to an embodiment of the present invention;

FIG. 2 a measurement system, another switch-extender and several DUTsaccording to an embodiment of the present invention;

FIG. 3 a detailed configuration of the plurality of firstMUX/DEMUX-units according to an embodiment of the present invention;

FIG. 4 a detailed configuration of the plurality of secondMUX/DEMUX-units according to an embodiment of the present invention;

FIG. 5 a 3-dimensional view of the exemplary embodiment of theswitch-extender 4 according to the present invention;

FIG. 6 another detailed configuration of the plurality of secondMUX/DEMUX-units sharing the output ports of each other according to anembodiment of the present invention;

FIG. 7 a flow chart diagram of a test routine according to an embodimentof the present invention;

FIG. 8 a measurement system, a switch-extender and a calibration systemaccording to an embodiment of the present invention;

FIG. 9 a flow chart diagram of a calibration routine according to anembodiment of the present invention;

FIG. 10 another flow chat diagram of a further calibration routineaccording to an embodiment of the present invention;

FIG. 11 another flow chat diagram of a further calibration routineaccording to an embodiment of the present invention;

FIG. 12 another flow chat diagram of a further calibration routineaccording to an embodiment of the present invention; and

FIG. 13 another flow chat diagram of a further calibration routineaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

In the following some preferred embodiments of the present invention aredescribed in detail.

FIG. 1 shows the basic principle of the present invention. It shows ameasurement system 1 which is used for generating a test signal(downlink signal) and which is also used for measuring a signaltransmitted from the DUTs (uplink signal). Therefore, the measurementsystem 1 comprises a TRX unit 2 (transmit receive) which is used forgenerating the base band and/or the RF (radio frequency). Furthermorethe measurement system 1 also comprises a frontend 3 which comprises areference circuit and which divides the signal from or to the TRX unit 2into three input or output ports. For example, there is a first port“RF1Out” which is used to output the test signal (downlink signal) thatis normally a high frequency signal, like a GSM or UMTS (CDMA signal ingenerally). Furthermore, there is a second port “RF1COM” which is usedto output the test signal (downlink signal) or which can be used as aninput port for a signal (uplink signal) that is transmitted by themobile communication system to be measured by the measurement system 1.Furthermore, there is a third port “RF2COM” which can also be used tooutput the test signal (downlink signal) and which can also be used toinput a signal (uplink signal) transmitted from the mobile communicationsystem 7 (device under test-DUT).

However, all three ports “RF1Out”, “RF1COM” and “RF2COM” are connectedto a switch-extender 4 according to the embodiment of the presentinvention. The switch-extender 4 comprises a first MUX/DEMUX-unit 5having a ratio of one to eight. The switch-extender 4 according to thepresent invention may also have a second MUX/DEMUX-unit 6 which has aratio of one to four. The second MUX/DEMUX-unit 6 is optional. However,other ratios are also possible. The switch-extender 4 will be describedin the following in detail.

Furthermore, the switch-extender 4 is preferably connected to severalmobile communication systems 7, also called devices under test (DUT).This connection is done by using a cable connection. In this case, thereare four devices under test, also called DUTs 7 ₁, 7 ₂, 7 ₃, 7 ₄. Asmentioned before, the DUTs can be a mobile phone or a handheld PC or atablet PC or a pocket PC or even a WLAN router. For this example, eachof the DUTs 7 ₁, 7 ₂, 7 ₃, 7 ₄ has at least three antennas. However, itis possible that a DUT 7 ₁, 7 ₂, 7 ₃, 7 ₄ has also more or less thanthree antennas. FIG. 1 also shows that two antennas of each DUT 7 ₁, 7₂, 7 ₃, 7 ₄ are connected to the MUX/DEMUX-unit 5 of the switch-extender4. Those antennas are used for communication by using the MIMO (MultipleInput, Multiple Output) technique. A third antenna of each DUT 7 ₁, 7 ₂,7 ₃, 7 ₄ is connected to the second MUX/DEMUX-unit 6. The third antennacan be used for GPS or WLAN. It can also be used for Bluetooth or othercommunication standards.

The antennas of the DUT 7 ₁, 7 ₂, 7 ₃, 7 ₄ and the cable connection arenot matched. Therefore, an attenuator is used between the cable and theantenna. Normally a 3 dB attenuator is used as shown in FIG. 1. Using a3 dB attenuator, the reflected wave from the antenna of the DUT has asignal level which is 6 dB lower than the signal level of the signal(downlink) which is transmitted from the measurement system 1 over theswitch-extender 4 to the antennas of the DUT 7 ₁, 7 ₂, 7 ₃, 7 ₄.

The second MUX/DEMUX-unit 6 is only used for none-cellular applicationslike WLAN, Bluetooth or GPS or the like. If the DUT uses only oneantenna for cellular applications (none-MIMO) the switch-extender 4 cansupport up to eight DUTs.

If the second MUX/DEMUX-unit 6 is used, the none-cellular applications(WLAN, Bluetooth and/or GPS) are tested first, since the cellular chips(CDMA-chips) need more time to come up. The measurement system 1generates a base band-signal (downlink) in the TRX-unit 2. This signal(downlink) is then sent to the MUX/DEMUX-unit 6 using the third port“RF2COM” of the second MUX/DEMUX unit 6. The second MUX/DEMUX-unit 6connects the third port of the measurement system 1 to the third antennaof the first DUT 7 ₁. After the test signal is sent, the first DUT 7 ₁is processing it. After the first DUT 7 ₁ has processed the test signal,it outputs the results, for example the current GPS-position using thethird antenna or a data bus which is not shown. The secondMUX/DEMUX-unit 6 still connects the third antenna to the third port“RF2COM” of the measurement system 1. The measurement system 1 cananalyze if the calculated results of the first DUT 7 ₁ are correct. Ifthe none-cellular applications are tested for the first DUT 7 ₁, thesecond MUX/DEMUX-unit 6 connects the third port of the frontend 3 of themeasurement system 1 to the third antenna of the second DUT 7 ₂.

The second MUX/DEMUX-unit 6 connects all DUTs 7 ₁, 7 ₂, 7 ₃, 7 ₄ oneafter another to the third port of the measurement system 1. The secondMUX/DEMUX-unit 6 can also connect DUTs to another port of themeasurement system 1 as long as this port can also be used fortransmitting and receiving signals. In this case, the secondMUX/DEMUX-unit 6 can also be connected to the second port “RF1COM” ofthe measurement system 1.

If the measurement of the none-cellular applications of the DUTs 7 ₁, 7₂, 7 ₃, 7 ₄ is done, the cellular chips of the DUTs 7 ₁, 7 ₂, 7 ₃, 7 ₄are up for operation. Now the measurement system 1 generates andtransmits test signals to the first MUX/DEMUX-unit 5. The signals aregenerated in the TRX-unit 2 and are sent by using the first port“RF1OUT” of the frontend 3. This test signal is then split into eightsignals and transmitted to the first and to the second antenna of eachof the four DUTs 7 ₁, 7 ₂, 7 ₃, 7 ₄. The test signal can comprise areally long sequence that is used to calculate the bit error rate (BER)of each of the DUTs. So each of the DUTs 7 ₁, 7 ₂, 7 ₃, 7 ₄ receives along sequence which is used to calculate the bit error rate. If the DUTshave calculated the bit error rate, the first MUX/DEMUX-unit 5 connectsone DUT after another to the second port “RF1COM” of the measurementsystem 1. The measurement system 1 then measures the uplink signal fromeach of the DUTs 7 ₁, 7 ₂, 7 ₃, 7 ₄.

FIG. 2 shows a measurement system 1 which comprises two separateTRX-units 2, 8 and two separate frontends 3, 9. Furthermore, theswitch-extender 4 also comprises a first MUX/DEMUX-unit 5 and optionallya second MUX/DEMUX-unit 6 as described above. Furthermore, theswitch-extender 4 comprises also a further MUX/DEMUX-unit 10 having alsoa ratio of one to eight and a MUX/DEMUX-unit 11 having a ratio of one tofour. The MUX/DEMUX-unit 11 is also optional. Therefore, several otherDUTs 12 ₁, 12 ₂, 12 ₃, 12 ₄ are connected to the further MUX/DEMUX-unit10 and to the MUX/DEMUX-unit 11 as described above referring to the DUTs7 ₁, 7 ₂, 7 ₃, 7 ₄.

FIG. 3 shows a detailed schematic diagram of the first MUX/DEMUX-unit 5according to the present invention. It can be seen that the firstMUX/DEMUX-unit 5 is divided into two parts. The first part is thetransmission path and the second part is the receiving path. Thetransmission path is used to transmit a signal (downlink signal) frommeasurement system 1 to the DUTs 7 ₁ to 7 ₄ in parallel and thereceiving path is used to transmit a signal (uplink signal) from theDUTs 7 ₁ to 7 ₄ to the measurement system 1. The transmission path isconnected to the first port “RF1Out” of the frontend 3 of themeasurement system 1.

The downlink signal is split using a signal splitter 30, like aWilkinson divider, into two signals, both having preferably the samesignal level. Each output port of the signal splitter 30 is thenconnected to a switch 31 ₁, 31 ₂. One output port of each switch 31 ₁,31 ₂ is not connected to anything, so the switch can be used to decouplethe specific signal path at all. Normally the other output port of theswitch 31 ₁, 31 ₂ is used to connect each output of the signal splitter30 to an amplifier 32 ₁, 32 ₂. The amplifiers 32 ₁, 32 ₂ can be used toamplify the signal by 0 to +20 dB. The output of each of the amplifiers32 ₁, 32 ₂ is then connected to another signal splitter 33 ₁, 33 ₂. Eachoutput port of the further signal splitters 33 ₁, 33 ₂ is then connectedwith another signal splitter 34 ₁, 34 ₂, 34 ₃, 34 ₄. The downlink signalwhich is generated by the TRX-Unit 2 is split up and amplified intoeight equal signals. Those signals can be used for four DUTs 7 ₁, 7 ₂, 7₃, 7 ₄, each of them having up to two cellular antennas operating inMIMO-mode.

However, before the eight individual downlink signals can be sent to theDUTs 7 ₁, 7 ₂, 7 ₃, 7 ₄ they are applied to a level adjustment unit 35.The level adjustment unit 35 is very important, because it comprisesseveral attenuators. Each signal path that is used for carrying one ofthe split downlink signals comprises two attenuators arranged in series.Therefore, each output port of the further signal splitters 34 ₁, 34 ₂,34 ₃, 34 ₄ is connected to a first attenuator 36 ₁, 36 ₂, 36 ₃, 36 ₄, 36₅, 36 ₆, 36 ₇ and 36 ₈. Those first attenuators 36 ₁ are 36 ₈ are alsocalled step-attenuators. Those attenuators can be used to attenuate thesplit downlink signal in steps of approximately ¼ dB from 0 to 31 dB.The output port of each the first attenuators of each signal path isthen connected to a second attenuator 37 ₁, 37 ₂, 37 ₃, 37 ₄, 37 ₅, 37₆, 37 ₇ and 37 ₈. The second attenuators are also called fineattenuators. They allow attenuating the split downlink signal in stepsof approximately a 2 mdB.

Each output port of the level adjustment unit 35 or, to be more precise,each output port of the second attenuator is connected to onecoupling-unit 38 ₁ to 38 ₈. The use of each coupling-unit is that thedownlink signal which is split into up to eight individual downlinksignals is transmitted to the first and to the second antenna of eachDUT and that the uplink signal which is transmitted from the first andthe second antenna of each DUT is transmitted back to the second outputport “RF1COM” of the measurement system 1. Therefore, the coupling-unit38 ₁ to 38 ₈ prevents an uplink signal which is transmitted from theDUTs to travel across the downlink signal path. The coupling-unit 38 ₁to 38 ₈ is preferably a directional coupling-unit 38 ₁ to 38 ₈, so thatthe uplink signal exits the directional coupling-unit 38 ₁ to 38 ₈through another port. The directional coupling-unit 38 ₁ to 38 ₈comprises three attenuators and three resistors, for example connectedin a T-structure. Each output port RF1 to RF8 is connected to the firstor to the second antenna of each DUT 7 ₁, 7 ₂, 7 ₃, 7 ₄ using a cableand several connectors.

The task of the switch-extender 4 according to the present invention isthat the downlink signal at the first and the second antenna of each ofthe DUTs 7 ₁, 7 ₂, 7 ₃, 7 ₄ has the same predetermined signal level. Soall downlink signals that apply at the cellular antennas of each DUThave the same level. In order to obtain this object, the attenuation ofthe cable and the connectors have to be taken into account. This objectis solved by the use of the level adjustment unit 35. The leveladjustment unit 35 allows a coarse and a fine tuning of the splitdownlink signals. Since the first and the second attenuator within thelevel adjustment unit 35 are built by using transistors or the like, thesignal can be attenuated within 300 microseconds or less. Relays whichare used in the state of the art are preferably not used within thepresent invention at all.

The signal level of the downlink signal is very low, for example −100dBm. The third output ports RX1 to RX8 of each of the coupling-units 38₁ to 38 ₈ are connected to a multiplexer 39 ₁, 39 ₂. Each of themultiplexers 39 ₁, 39 ₂ have four input ports for example and one outputport. Therefore, the uplink signal which is transmitted from the firstand the second DUT 7 ₁, 7 ₂ is available at the first multiplexer 39 ₁and the uplink signal which is transmitted from the third and the fourthDUT 7 ₃, 7 ₄ is available at the second multiplexer 39 ₂. This is doneby using the coupling-units 38 ₁ to 38 ₈ as described above.

The output port of each multiplexer 39 ₁, 39 ₂ is connected to anotherattenuator 40 ₁, 40 ₂. These attenuators 40 ₁, 40 ₂ are able toattenuate an uplink signal coarsely. In this example according to thepresent invention the attenuators 40 ₁, 40 ₂ can attenuate an uplinksignal in steps of 0 dB, −13 dB and −26 dB. It is also possible to usean attenuator 40 ₁, 40 ₂ which attenuates an uplink signal in muchsmaller steps. If the DUT 7 ₁, 7 ₂, 7 ₃, 7 ₄ transmits an uplink signalhaving a signal level of 33 dBm for example, the attenuation factor ofthe attenuator 40 ₁, 40 ₂, is selected to the highest possible value, inthis example −26 dB. If the DUT transmits an uplink signal with a signallevel of 0 dBm the attenuator 40 ₁, 40 ₂ selects the lowest possibleattenuation factor, in this example 0 dB.

The output port of each of the attenuators 40 ₁, 40 ₂ is connected to anamplifier 41 ₁, 41 ₂. Each amplifier 41 ₁, 41 ₂ amplifies the inputsignal to an output signal having a desired signal level. The amplifierfactor is chosen so that the measurement system 1 measures the uplinksignal with the highest possible precision.

The output port of each amplifier is connected to a switch 42. By usingthe switch 42 and one of the multiplexer 39 ₁, 39 ₂ a control unitwithin the switch-extender 4 or within the measurement system 1 selectsthe uplink signal from one antenna of one of one DUT 7 ₁, 7 ₂, 7 ₃, 7 ₄to be measured within the measurement system 1. The output port of theswitch 42 is then connected to the second port “RF1COM” of themeasurement system 1. It can also be connected to the third port“RF2COM” or to any port within the measurement system 1 which allowsinputting an uplink signal for further analyses.

However, the schematic diagram of FIG. 3 can also be used within thefurther MUX/DEMUX-unit 10 as shown in FIG. 2.

The level adjustment unit 35 selects an attenuation value for the firstattenuators 36 ₁ to 36 ₈ and for the second attenuators 37 ₁ to 37 ₈which is based on the individual cable and connectors as well as on theindividual signal path. The correction data is obtained for eachfrequency point for each signal path as well as for each cable andconnector. Therefore, if the frequency band for which the downlinksignal is transmitted is changed, all attenuators within the leveladjustment unit 35 have to be set for their new attenuation factor.

Furthermore, the amplifiers 32 ₁, 32 ₂ and 41 ₁, 41 ₂ as well as theattenuators 40 ₁, 40 ₂ may also need to be set for the new frequency.This is done preferably very fast in less than 300 microseconds. Thecontrol of the level adjustment unit 35 as well as of the amplifiers 32₁, 32 ₂, as well as of the amplifiers 41 ₁, 41 ₂ and as well as of theattenuator 40 ₁, 40 ₂ can be done in three different ways.

First of all, the aforementioned components can be connected to themeasurement system 1 directly. However, only very fast connection typesare recommended. This could be done by an interface with a lot ofparallel data lines applying a high clock rate. The measurement system 1selects all attenuation factors as well as all amplifier factors for theselected frequency of operation of the downlink signal. This informationcan be extracted from calibration data which will be discussed below.SPI-commands allow those components to be programmed by the measurementsystem 1.

A more preferred second possibility for adjusting the aforementionedcomponents can be done by incorporating a processing unit 45 within theswitch-extender 4. The processing unit is connected to the leveladjustment unit 35 and therein with the first attenuators and the secondattenuators. The processing unit 45 is further connected to theamplifier 32 ₁, 32 ₂, 41 ₁, 41 ₂ as well as to the attenuators 40 ₁, 40₂ and optional to the multiplexers 39 ₁, 39 ₂ and the switches 31 ₁, 31₂, 42. Furthermore, the processing unit is also connected to themeasurement system 1. The measurement system 1 then signals theprocessing unit 45 the values of the attenuation and/or theamplification factors to be set and optional the position of theswitches and the multiplexers. The communication itself between theprocessing unit 45 and the components within the switch-extender 4 isdone without any knowledge of the measurement system 1. For example, theprocessing unit 45 can communicate by using the SPI-commands on a singleline or by using parallel data lines.

A third possibility is that the processing unit 45 only receives thefrequency and the signal level of the downlink signal which istransmitted by the measurement system 1. The processing unit 45 thenalternates all attenuation factors or amplification factors by itself.Therefore, besides the processing unit 45 a further storage unit 46 isneeded where all calibration data are stored. This could be done byusing a lookup-table comprising all attenuation factors and/oramplification factors needed for an individual signal level as well asfor an individual signal frequency. The processing unit 45 then readsout the storage unit 46 and alternates those factors as required.

As shown in FIG. 3 it is possible to transmit a downlink signal on eightsignal paths in parallel. On the other hand, it is only possible toreceive one uplink signal which is transmitted from one antenna of oneDUT 7 ₁, 7 ₂, 7 ₃, 7 ₄ at one time. In order to receive the uplinksignal from the other antenna or from other DUTs the multiplexer 39 ₁,39 ₂ or the switch 42 have to be changed. This can also be done by theprocessing unit 45 or by the measurement system 1 directly. Therefore,the multiplexer 39 ₁, 39 ₂ as well as the switch have to be connected tothe processing unit 45 and/or to the measurement system 1. This can alsobe done by well known data connection types or by a parallel interface.The same also applies for the further MUX/DEMUX-unit 10.

FIG. 4 shows a schematic diagram of the second MUX/DEMUX-unit 6 as wellas of the MUX/DEMUX-unit 11 according to the present invention. Asalready described, the second MUX/DEMUX-unit 6 is used to measure thenone-cellular applications within the DUT 7 ₁, 7 ₂, 7 ₃, 7 ₄. As alreadyexplained, the measurement system 1, in particular the TRX-unit 2 andthe frontend 3 generate a downlink signal which is output at the thirdoutput port “RF2COM”. For the second TRX-unit 8 and the second frontend9 the subject matter as explained in detail above stays the same. Itonly differs in the names used for the reference signs. As already said,the third port “RF2COM” can be used to output a downlink signal or toinput an uplink signal. In the following the case where a downlinksignal is transmitted to the third antenna of the DUT 7 ₁, 7 ₂, 7 ₃, 7 ₄is described. The output port “RF2COM” is connected to a switch 50. Oneoutput port of the switch 50 is connected to another switch 51. Oneoutput of the switch 51 is connected to an amplifier 52. The amplifier52 is used to amplify the downlink signal by 0 to +20 dB. The output ofthe amplifier 52 is connected to a signal splitter 53. The signalsplitter 53 can be a Wilkinson divider.

Each output port of the signal splitter 53 is connected to an input portof another signal splitter 54 ₁, 54 ₂. Each output port of the furthersignal splitters 54 ₁, 54 ₂ is connected to the second level adjustmentunit 55. The second level adjustment unit 55 comprises the samestructure as the level adjustment unit 35 as described in FIG. 3. Incontrast to the level adjustment unit 35 as described in FIG. 3, thesecond level adjustment unit 55 only comprises four signal paths. Ineach signal paths, there are two attenuators arranged in series. A firstattenuator 56 ₁, 56 ₂, 56 ₃, 56 ₄ is used to attenuate the splitdownlink signal in a coarse step. For example, the first attenuator 56 ₁to 56 ₄ can attenuate the split downlink signal in steps of ¼ dB over arange from 0 to 31 dB. The output port of the first attenuator 56 ₁ to56 ₄ is then connected to an input port of a second attenuator 57 ₁, 57₂, 57 ₃, 57 ₄. The second attenuator is used to attenuate the splitdownlink signal in finer steps. For example, the second attenuators 57 ₁to 57 ₄ can attenuate a signal in steps of 2 mdB or the like. The outputport of the second attenuators 57 ₁ to 57 ₄ is then connected to acoupling-unit 58 ₁ to 58 ₄. The design of the coupling-unit 58 ₁ to 58 ₄as shown in FIG. 4 is the same as the design of the coupling-unit 38 ₁to 38 ₈ as shown in FIG. 3 so that a reference is made to thedescription above. The second output port RF1 to RF4 of thecoupling-unit 58 ₁ to 58 ₄ is connected to the third antenna of the DUTs7 ₁, 7 ₂, 7 ₃, 7 ₄.

If the measurement system 1 generates and transmits a downlink signal tothe third antenna of all DUTs 7 ₁, 7 ₂, 7 ₃, 7 ₄ the second leveladjustment unit 55 makes sure that the level of the downlink signal isthe same for all signal paths at the third antenna of each DUT 7 ₁, 7 ₂,7 ₃, 7 ₄. This is done by using calibration data of the cable and theconnector as well as of each individual signal path. The amplificationas well as the attenuation value of each attenuator is selected in sucha way that different frequency behaviors over a frequency span arecompensated. This also applies for different signal levels. Therefore,every downlink signal frequency and every downlink signal levelcorresponds to a separate data set which includes the calibration datathat is used for setting the amplifier 52 and the first attenuator 56 ₁to 56 ₄ and the second attenuator 57 ₁ to 57 ₄ properly.

The same also applies for every uplink signal. The uplink signaltransmitted from the third antenna of each DUT 7 ₁, 7 ₂, 7 ₃, 7 ₄ isdecoupled within the coupling-unit 58 ₁ to 58 ₄ to the third output portRX1 to RX4. The third output port RX1 to RX4 of all coupling-units 58 ₁to 58 ₄ are connected to a multiplexer 59. The multiplexer has fourinput ports connected to each of the coupling-units 58 ₁ to 58 ₄ and oneoutput port connected to an attenuator 60. The attenuator 60 attenuatesthe uplink signal in a coarse way. For example, an attenuation factor of0, −13, −26 dB can be selected. However, also other attenuators can beused which allow the selection of an attenuation factor having finersteps. The output port of the attenuator 60 is then connected to theinput port of an amplifier 61. The amplifier 61 is then connected to thesecond “output” port of the switch 50. The switch 50 then connects theoutput port of the amplifier 61 to the third port “RF2COM” of themeasurement system 1. The attenuator 60 is thereby selected to attenuatea strong signal with a higher attenuation factor than a weak signal. Forexample, if the DUT transmits an uplink signal having a signal level 30dB, the attenuator 60 attenuates this signal by −26 dB. On the otherhand, if the DUT transmits a signal having a signal level of 0 dB, theattenuator 60 attenuates this signal with 0 dB. Other values are alsopossible.

As already described in FIG. 3 the amplifiers 52, 61 and the attenuators56 ₁ to 56 ₄ and 57 ₁ to 57 ₄ and 60 are controlled by the measurementsystem 1 directly or by the processing unit 45. The same also appliesfor the switch 50, the switch 51 and the multiplexer 59. The switch 51can be used to separate the transmitting path from the receiving path inorder to increase the isolation between them.

As already explained, the components can be controlled by themeasurement system 1 directly. In this case, the measurement system 1sets all switch positions and/or all attenuation and/or amplificationfactors. On the other hand, the measurement system 1 can signal theprocessing unit 45 the switching positions and the amplification and/orattenuation factors. The third possibility is that the measurementsystem 1 only informs the processing unit 45 about the frequency and thesignal level of the downlink signal and/or the number of the DUT whichhas to be measured in the uplink path. The processing unit 45 then readsthe settings from a storage unit 46 and makes the needed adjustments.

The same also applies for the MUX/DEMUX-unit 11 as also shown in FIG. 4.For those components no reference signs are placed. However, allexplanations made to the second MUX/DEMUX-unit 6 are also valid for theMUX/DEMUX-unit 11.

FIG. 5 shows a 3-dimensional view of the exemplary embodiment of theswitch-extender 4 according to the present invention. Theswitch-extender 4 comprises a series of input and/or output ports. Theports for connecting the switch-extender 4 to the measurement system 1are located on the right side of the switch-extender 4. FIG. 5 shows theports “RF1Out”, RF1COM″ and “RF2COM” for connecting the switch-extender4 to the first frontend 3 within the measurement system 1. Furthermore,FIG. 5 also shows the ports “RF3Out”, “RF3COM” and “RF4COM” forconnecting the switch-extender 4 to the second frontend 9 within themeasurement system 1. In this exemplary embodiment, the ports forconnecting the switch-extender 4 to the measurement system 1 are shownon the right, but they can also be located anywhere on the front or therear-panel of the switch-extender 4.

The other ports are used for connecting the switch-extender 4 to theseries of antennas of the DUTs 7 ₁, 7 ₂, 7 ₃, 7 ₄ and 12 ₁ to 12 ₄. Forexample eight ports on the bottom row from left to right represent theoutput and/or input ports of the MUX/DEMUX-unit 5 as shown in FIG. 3.Within FIG. 3 these ports are named RF1 to RF8. The top row comprisesthe input and/or output ports for the further MUX/DEMUX-unit 10 which isconnected to the second frontend 9. With respect to FIG. 2, also eightports are used therefor. The row in the middle is used for the secondMUX/DEMUX-unit 6 as well as for the MUX/DEMUX-unit 11. In this exemplaryembodiment the four ports from left to right represent the output and/orinput ports of the second MUX/DEMUX-unit 6, whereas the four portsfollowing on the right represent the input and/or output ports of theMUX/DEMUX-unit 11. However, it is obvious that the input and/or outputports can be arranged in different ways. Beside every port, there aretwo LEDs 70 ₁, 70 ₂. Those LEDs 70 ₁, 70 ₂ indicate whether theindividual port is used as an output port or an input port.

All ports are mounted directly on a printed circuit board. Preferablythere are no cable connections. There is normally one printed circuitboard for each row using connectors to connect the individual printedcircuit boards together. All printed circuit boards are controlled by acentral processing unit 45. However, as described above, the ports canalso be controlled by the measurement system 1 itself.

FIG. 6 shows a further exemplary embodiment of a schematic diagramaccording to the present invention. According to FIG. 5 the outputand/or input ports in the middle of the row are shared between the firstfrontend 3 and the second frontend 9. One possibility on how to connectthese ports with the measurement system 1 is shown in FIG. 4. As alreadydescribed above, it is not possible for the first frontend 3 and for thesecond frontend 9 to use the output ports of the switch-extender 4 fromeach another. This means that the first frontend 3 can only address fourDUTs 7 ₁, 7 ₂, 7 ₃, 7 ₄ each having one third antenna. The same appliesfor the second frontend 9. The second frontend 9 can also only addressfour DUTs 12 ₁ to 12 ₄ each having one third antenna. However, some DUTsmay have more than three antennas. Therefore, it would be desirable ifthe first frontend 3 could also use the output and/or input ports of theswitch-extender 4 linked to the second frontend 9.

FIG. 6 describes a possibility that allows the first frontend 3 to usethe input and/or output ports of the second MUX/DEMUX-unit 6 as well asthe input and/or output ports of the MUX/DEMUX-unit 11. On the otherhand, FIG. 6 also shows the possibility for the second frontend 9 to usethe input and/or output ports of the MUX/DEMUX-unit 11 as well as theinput and/or output ports of the second MUX/DEMUX-unit 6.

As shown in FIG. 6, the port “RF2COM” is connected to a multiplexer 80and the port “RF4COM” is connected to a multiplexer 81. It is noted thatthe ports “RF2COM” and “RF4COM” are bidirectional ports which can beused as output ports as well as input ports. Therefore, the wording“multiplexer” is always used instead of the wording “demultiplexer”. Oneoutput port of the multiplexer 80 can be connected to the transmit pathas shown in FIG. 4. The transmit path comprises another switch 82 andthe well-known circuit elements 52, 53, 54 ₁, 54 ₂, 55 and 58 ₁ to 58 ₄.

A second output of the multiplexer 80 can also be connected to thesecond transmit path which was only used in FIG. 4 by the secondfrontend 9. The second output of the multiplexer 80 is thereforeconnected to a switch 83 and in row to the switch 83 to a signalsplitter 84. One outfit of the splitter 84 is connected to the switch 82and the other output of the signal splitter is connected to the switch85. The output of the switch 85 is thereby connected to the secondsignal path. The circuit elements of the second signal path are the sameas the circuit elements of the first signal path.

The same applies for the uplink signal, namely the signal which istransmitted from the third antenna of the DUT 7 ₁, 7 ₂, 7 ₃, 7 ₄ as wellas for the uplink signal which is transmitted from the third antenna ofthe DUT 12 ₁ to 12 ₄. As described in FIG. 4, coupling-units 58 ₁ to 58₄ are used to decouple the uplink signal transmitted by the thirdantenna of the DUT 7 ₁, 7 ₂, 7 ₃, 7 ₄. The uplink signal is decoupled atthe third port of the coupling-unit 58 ₁, to 58 ₄. These ports arecalled RX1 to RX4. These ports are connected to a multiplexer 59. Themultiplexer 59 selects one uplink signal at the same time and forwardsit to an attenuator 60. The output of the attenuator 60 is connected toan amplifier 61. This subject matter is also described with respect toFIG. 4. Within FIG. 6 the output of the amplifier 61 is connected to aswitch 86. The output of the switch 86 is connected to the multiplexer80.

The same also applies for the uplink path of the DUTs 12 ₁ to 12 ₄. Theuplink signal transmitted from the DUTs 12 ₁ to 12 ₄ is decoupled by thecoupling-units 87 ₁ to 87 ₄. Those coupling-units are integrated withina switch-extender 4 in the MUX/DEMUX-unit 11. The uplink signal is thenfed to a multiplexer 88. The multiplexer 88 selects one uplink signal atthe same time and forwards it to another attenuator 89. The output portof the attenuator 89 is then connected to an amplifier 90. The output ofthe amplifier 90 is further connected to switch 91. One output of theswitch 91 is also connected to the multiplexer 80. The multiplexer 88 isthe same multiplexer as the multiplexer 59. The attenuator 89 is thesame attenuator as the attenuator 60. The amplifier 90 is the sameamplifier as the amplifier 69. This also applies for coupling-units 87 ₁to 87 ₄ with respect to the coupling-units 58 ₁ to 58 ₄.

The aforementioned structure allows the first frontend 3 to address thethird antenna of the DUTs 7 ₁ to 7 ₄ and 12 ₁ to 12 ₄. The firstfrontend 3 can transmit a downlink signal to all third antenna ports ofthe DUTs 7 ₁, to 7 ₄ and 12 ₁ to 12 ₄ at the same time. However, theuplink signal from the third antenna of every DUT 7 ₁, 7 ₂, 7 ₃, 7 ₄ and12 ₁ and 12 ₄ can be fed through the input port “RF2COM” to the firstfrontend 3 one after another. The same also applies for the secondfrontend 9. The bidirectional port “RF4COM” is connected to themultiplexer 81 as described above. The output ports of the multiplexer81 are connected to the switch 83 as well as to the switch 85 as well asto the switch 86 and to the switch 91. Therefore, it is also possiblefor the second frontend 9 to address all third antenna ports of all DUTs7 ₁ to 7 ₄ and 12 ₁ to 12 ₄. The second frontend 9 can thereforetransmit the downlink signal to all DUTs 7 ₁ to 7 ₄ and 12 ₁ and 12 ₄ atthe same time. The uplink signal transmitted from each DUT at the thirdantenna board can be measured one after another by switching themultiplexer 59 and 88 as well as the switches 86 and 91 as well as themultiplexer 81 accordingly.

To sum it up, the above described structure of the switch-extender 4having further multiplexers 80, 81 for each of the plurality of thesecond MUX/DEMUX-units 6 that are connected to every downlink path andto every uplink path used by the second MUX/DEMUX-units 6 allows theplurality of the second MUX/DEMUX-units 6, 11 to access all componentswithin the uplink path as well as within the downlink path of each otherthereby doubling the available output ports.

However, all components like the switches, the amplifiers, theattenuators, the multiplexers can be controlled directly by themeasurement system 1 or they can be controlled by a processing unit 45.The subject matter is described in detail above so that a reference ismade thereto.

FIG. 7 shows a flow chart diagram that describes the proceeding fortesting several DUTs with the switch-extender 4 and the measurementsystem 1 according to the present invention. After all DUTs areconnected to the switch-extender 4, the procedural step S₁ is executed.Within the step S₁ all DUTs are powered up and the non-cellularcomponents of all DUTs are tested. As described above, those componentsare connected to the third antenna of each DUT. For example, in the stepS₁ Bluetooth services, GPS services or WLAN services can be tested. Asalready explained in detail, it is also possible that the measurementsystem 1 transmits a downlink signal to all DUTs 7 ₁ to 7 ₄ and/or 12 ₁to 12 ₄ simultaneously. After that the third antenna of each DUT isconnected one after another with the measurement system 1 for measuringthe uplink signal.

If the non-cellular components are tested, the procedural step S₂ isexecuted. The procedural step S₂ is preferably executed when thecellular components are booted. The cellular components comprise forexample CDMA-chips. Those chips have a longer boot time than thenon-cellular components. Within the procedural S₂ a downlink signal issent from the measurement system 1 to all DUTs 7 ₁ to 7 ₄ and 12 ₁ to 12₄ which comprises a long data sequence. This sequence is well known andallows the DUTs to calculate the bit error rate for example. In order toobtain a good statistic, the sequence is transmitted over a longerperiod, for example 10 seconds.

After the bit error rate is calculated by all DUTs in parallel for adesired frequency and/or for desired signal level, the procedural stepS₃ is executed. Within the procedural step S₃ the procedural step S₂ isrepeated for all desired frequency bands and/or for all desired signallevels. The DUTs further calculate the bit error rate.

Afterwards the procedural step S₄ is executed. Within the proceduralstep S₄, the measurement system 1 collects all calculated BER-values forone DUT after another. This is done by decoupling the uplink signalwhich is transmitted from the DUT by using the coupling-unit 58 ₁ to 58₄ and 87 ₁ to 87 ₄. As already described each frontend 3, 9 can onlyreceive one uplink signal at the same time. However, the time forcollecting the calculated BER-values is much shorter than the time forsending the sequence to all DUTs. Therefore, it does not matter that allDUTs cannot transmit the uplink signal at the same time.

In the following, the procedural step S₅ is executed. Within theprocedural step S₅, the reception for every DUT is calibrated inparallel or one after another for the desired frequency. This is done byusing the method and the system which is described in the U.S. patentapplication US 2009/0209249 A1 which is hereby incorporated byreference. The time between the steps wherein the signal level islowered has to be as long as the time it needs to adjust the attenuatorsand the amplifiers. 300 microseconds should be enough.

Afterwards, the procedural step S₆ is executed. In the procedural StepS₆, the step S₅ is repeated for all desired frequency bands.

After that, the procedural step S₇ is executed. Within the proceduralstep S₇ all DUTs are calibrated one after another for their transmissionbehavior. The method and the system that are used therefore are alsodescribed in the U.S. patent application US 2009/0209249 A1 which ishereby incorporated by reference. Each frontend 3, 9 receives only oneuplink signal at the same time. The uplink signal is thereby steppeddown continuously. However, the time for each step has to be chosen insuch a way that the switch-extender 4 has enough time to adjust thesettings for the attenuators, the amplifiers and the switches. This isdone for all DUTs one after another.

Afterwards, the procedural step S₈ is executed. Within the proceduralstep S₈ the former step S₇ is repeated for all desired frequency bands.

Last but not least, a Pass/Fail-analysis is performed within theprocedural step S₉.

It has to be noted that procedural steps S₁ to S₉ need not to beexecuted in the described order. For example, it is also possible thatthe method is finished after the procedural step S₁ or after theprocedural step S₃ or after the procedural step S₈. The order can alsobe mixed.

FIG. 8 shows a schematic diagram that describes how the measurementsystem 1, the switch-extender 4 and the cable connection 100 ₁ to 100 ₄as well as the 3 dB attenuator 101 ₁, 101 ₂ are calibrated. Thecalibration is done by using a calibration system 102. The calibrationsystem comprises a first measurement unit 103 and a second measurementunit 105. Both measurement units 1, 5 are connected together for exampleby using a USB-connection. Other connection methods can also be used.The calibration system 102 further includes a signal splitter 104. Thesignal splitter 104 divides an input signal into two equal outputsignals. The first measurement unit 103 is able to measure and toanalyze a downlink signal as well as to generate a known uplink signal.In fact, the measurement unit 103 can be of the same type as themeasurement system 1. The second measurement unit 105 is able to measurethe signal power. The measured values are then transmitted to the firstmeasurement unit 1 by using the USB-connection. However, it is alsopossible that the DUT 7 ₁ to 7 ₄ and 12 ₁ to 12 ₄ is directly connectedwith the cable 100 ₁ to 100 ₄, so that no 3 dB attenuator 101 ₁, 101 ₂is needed.

Furthermore instead of using a cable 100 ₁ to 100 ₄ for establishing theconnection other signal connectors like wave guides for example can alsobe used.

In the following it is described how the calibration is done. The objectof the calibration is to determine the necessary settings within themeasurement system 1 and the switch-extender 4 in order to generate apredefined signal level at the first or at the second or at the thirdantenna of the DUT. It has to be noted that all cables 100 ₁ to 100 ₄ aswell as all connectors and the attenuators 101 ₁, 101 ₂ which are usedwithin the calibration also have to be used in the later measurementsteps.

Thus it is very important that every output port of the switch-extender4 has its own dedicated cable. The output ports of the MUX/DEMUX-unit 5as well as of the second MUX/DEMUX-unit 6 are connected one afteranother with the calibration system 102. The same also applies to thefurther MUX/DEMUX-unit 10 as well as for the MUX/DEMUX-unit 11. FIG. 10only describes the calibration method for the MUX/DEMUX-unit 5 withinthe switch-extender 4 having eight output ports. The first output portof the MUX/DEMUX-unit 5 which is labeled with “RF1” according to FIG. 3is connected to a cable 100 ₁. The other end of the cable 100 ₁ isconnected to a 3 dB attenuator 101 ₁. The attenuator 101 ₁ wouldnormally be connected with the first antenna of the first DUT 7 ₁. Inthis case, the other end of the attenuator 101 ₁ that is not connectedto the cable 100 ₁ is thereby connected with the calibration system 102.More exactly, the attenuator 101 ₁ is connected with the input of thesignal splitter 104 within the calibration system 102.

In the first instance, the measurement system 1 generates a downlinksignal which would normally be used to measure the proper functioning ofthe first antenna of the first DUT 7 ₁. The measurement system 1generates this downlink signal having a specific frequency as well as aspecific signal level. The downlink signal is split within the signalsplitter 104 into two equal signals. One signal is transmitted to thefirst measurement unit 103 whereas the other signal is transmitted tothe second measurement unit 103. It has to be understood that the signalsplitter 14 has to be well known when thinking of its attenuation or itsdiversity. However, the first measurement unit 103 and the secondmeasurement unit 105 measure the downlink signal properties, for examplethe frequency as well as the signal at the input port of the signalsplitter 104. This data is used in order to inform the measurementsystem 1 about the difference between the measured values of thedownlink signal and the estimated values of the downlink signal. Thisinformation is then used within the measurement system 1 to generatecalibration data in order to generate a downlink signal which has apredetermined frequency as well as a predetermined signal level at theantenna port of the DUT. The calibration data can also be generated thecalibration system 102.

After the calibration system 102 has generated the calibration data forthe downlink signal, the calibration data for the uplink signal has alsoto be generated. The uplink signal as well as the downlink signal shouldbe similar to the real signal. The uplink signal is generated by thefirst measurement unit 103. The first measurement unit 103 outputs theuplink signal to the signal splitter 104. One output port of the signalsplitter 104 is still connected to second measurement unit 105 which isalso connected the first measurement unit 103 by using a standardconnection for data transmission, like USB or the like. The other outputport of the signal splitter 104 is still connected with the cable 100 ₁over the 3 dB attenuator 101 ₁. It is very advantageous that the cableconnection has not to be changed for generating calibration data for theuplink signal. The second measurement unit 105 also measures the uplinksignal generated by the first measurement unit 103 and makes sure thatthe uplink signal has the dedicated signal frequency as well as thededicated signal level at the output port of the signal splitter 104.The uplink signal travels through the attenuator 101 ₁ and the cable 100₁ through the switch-extender 4 into the measurement system 1.

The measurement system 1 measures the signal frequency as well as thesignal level. Based on the difference between the measured uplink signalwithin the measurement system 1 and the measured uplink signal at theoutput port of the signal splitter 105, the calibration data is obtainedby the calibration system 102 or by the measurement system 1. Thecalibration data takes into account the downlink signal path as well asthe uplink signal path. The calibration data is obtained for severalfrequencies as well as for several signal levels. Based on thecalibration data, the measurement system 1 as well as theswitch-extender 4 know how to set the attenuators, the amplifiers asshown in FIG. 3 or FIG. 4 in detail. After the first cable 100 ₁ iscalibrated together with the attenuator 101 ₁ and all connectors, thesecond cable 100 ₂ together with the second attenuator 101 ₂ isconnected to the input port of the signal splitter 104 of thecalibration system 102. Then the calibration data is obtained for thesecond cable 100 ₂ as well as the attenuator 101 ₂. This is done for thedownlink signal as well as for the uplink signal as described above fora specific frequency as well for a specific signal level.

The aforementioned steps are repeated for all cables 100 ₁ to 100 ₄ thatare used for the MUX/DEMUX-unit 5 as well as for the secondMUX/DEMUX-unit 6 and for the further MUX/DEMUX-unit 10 as well as forthe MUX/DEMUX-unit 11.

FIG. 9 shows a flow chat diagram of a calibration routine according tothe present invention. The calibration routine has already beendescribed to a certain extent. In a procedural step S₁₀ the connectionsbetween the switch-extender 4 and the calibration system 102 areestablished. Those connections can be established by using a signalconnector 100 ₁ to 100 ₄ like a cable 100 ₁ to 100 ₄ or a wave guide orthe like. The signal connector 100 ₁ to 100 ₄ can be connected directlyto the calibration system 102 or through an attenuator 101 ₁, 101 ₂ likea 3 dB attenuator.

In the following the procedural step S₁₁ is executed. In this step asignal with a specific signal level and/or a specific signal frequencyis generated and output by the measurement system 1 for testing thedownlink path. Since the measurement system 1 is connected through theswitch-extender 4 and the signal connector 100 ₁ to 100 ₄ to thecalibration system 102, the output signal can be measured by thecalibration system 102.

This is done within the procedural step S₁₂. The calibration system 102measures the signal level and/or the signal frequency at the output ofthe signal connector 100 ₁ to 100 ₄ or at the output of the attenuator101 ₁, 101 ₂ if used.

In the following the procedural step S₁₃ is executed. Within theprocedural step S₁₂ a difference between the measured signal leveland/or the measured signal frequency and the generated signal with thespecific signal level and/or the specific signal frequency isdetermined. It is known by the calibration system 102 what signal leveland/or signal frequency should be obtained so that a deviation can becalculated.

In the next procedural step S₁₄ calibration data are calculated by usingthe determined difference between the measured signal level and/or themeasured signal frequency and the generated signal with the specificsignal level and/or the specific signal frequency. This can be done bythe calibration system 102 or even by the measurement system 1.

FIG. 10 shows a flow chat diagram of a calibration routine according tothe present invention. The calibration routine has already beendescribed to a certain extent.

In the following the procedural step S₁₅ is executed. It has to be notedthat the measurement system 1 and the switch-extender 4 are stillconnected to each other and to the calibration system 102. In this stepa signal with a specific signal level and/or a specific signal frequencyis generated and output by the calibration system 102 for testing theuplink path. Since the measurement system 1 is connected through theswitch-extender 4 and the signal connector 100 ₁ to 100 ₄ to thecalibration system 102, the output signal can be measured by themeasurement system 1. The calibration system 102 can also still measurethe generated signal by itself using the second measurement unit 105.

This is done within the procedural step S₁₆. The measurement system 1measures the signal level and/or the signal frequency at the output ofthe signal connector 100 ₁ to 100 ₄ or at the output of the attenuator101 ₁, 101 ₂ if used.

In the following the procedural step S₁₇ is executed. Within theprocedural step S₁₇ a difference between the measured signal leveland/or the measured signal frequency and the generated signal with thespecific signal level and/or the specific signal frequency isdetermined. It is known by the measurement system 1 what signal leveland/or signal frequency should be obtained so that a deviation can becalculated.

In the next procedural step S₁₈ calibration data are calculated by usingthe determined difference between the measured signal level and/or themeasured signal frequency and the generated signal with the specificsignal level and/or the specific signal frequency. This can be done bythe calibration system 102 or even by the measurement system 1.

FIG. 11 shows another flow chat diagram of a further calibration routineaccording to the present invention. The switch-extender 4 furthercomprises at least one attenuator 36 ₁, 36 ₂, 36 ₃, 36 ₄, 36 ₅, 36 ₆, 36₇, 36 ₈ or the at least one attenuator 36 ₁, 36 ₂, 36 ₃, 36 ₄, 36 ₅, 36₆, 36 ₇, 36 ₈ and a second attenuator 37 ₁, 37 ₂, 37 ₃, 37 ₄, 37 ₅, 37₆, 37 ₇, 37 ₈ in a row for every output port a signal connector 100 ₁ to100 ₄ is connected to the switch-extender 4. Thus a procedural step S₁₈can be executed. Within this step the attenuation factor of the at leastone attenuator 36 ₁ to 36 ₈ or adjusting the attenuation factor of theat least one attenuator 36 ₁ to 36 ₈ and the second attenuator 37 ₁ to37 ₈ can be adjusted so that the measured signal level and/or signalfrequency of the signal is equal to the generated signal with thespecific signal level and/or the specific signal frequency. Theprocedural step S₁₈ and the procedural steps S₁₂, S₁₃ and S₁₆, S₁₇ areexecuted alternately until the difference is smaller than a predefinedthreshold.

FIG. 12 shows another flow chart diagram of a further calibrationroutine according to the present invention. A procedural step S₂₀describes the previous steps are repeated for every desired frequencyand/or signal level. The step S₂₀ repeats the steps Generating,Measuring, Determining and Calculating for another signal frequencyand/or signal level or Repeating the steps Generating, Measuring,Determining, Adjusting and Calculating for another signal frequencyand/or signal level as described above.

FIG. 13 shows another flow chart diagram of a further calibrationroutine according to the present invention. The procedural steps S₂₁ andS₂₂ describe that after the calibration of one signal connector 100 ₁ to100 ₄ and the corresponding signal path for the downlink and the uplinkwithin the switch-extender 4 and optional for the attenuator 101 ₁, 101₂ another signal connector 100 ₁ to 100 ₄ is connected at another outputport of the switch-extender 4. After that the procedural steps S₂₂describes that the former steps Generating, Measuring, Determining andCalculating are repeated for another signal frequency and/or signallevel or that the former steps Generating, Measuring, Determining,Adjusting and Calculating are repeated for another signal frequencyand/or signal level.

In general, it is very important that the transmission path as well asthe receiving path comprise active components like attenuators oramplifiers which are built using transistors and/or discrete elementslike diodes for example or the like to compensate the loss in the signallevels. Furthermore, it is very important that those components havevery fast switching times so that the actual settings can be adjustedvery fast. This reduces the needed measurement time. This also allowsthat the signal level as well the signal frequency can be switched veryfast, since the correction of the attenuator as well as the amplifierstakes place in nearly no time.

It is also possible that further switch-extenders are connected to theswitch-extender 4 in order to obtain a measurement system 1 that allowsmeasuring more than eight DUTs having two antennas used in parallel forcellular applications. However, the specific arrangement shown above isnot limited to a measurement system 1 and a switch-extender 4 used foronly four DUTs. All features shown above can be combined together in anyorder.

What is claimed is:
 1. A method for calibrating a system comprising ameasurement system, a switch-extender, signal connects, attenuators andone calibration system comprising a first measurement unit, a secondmeasurement unit, and a signal splitter, wherein the method comprisesthe steps of: connecting a first output of the signal splitter to thefirst measurement unit; connecting a second output of the signalsplitter to the second measurement unit; connecting the first and thesecond measurement unit; connecting the switch extender to themeasurement system; connecting each one end of the several signalconnectors to the switch extender; connecting the other end of one ofthe several signal connectors with an attenuator to an input of thesignal splitter; generating a signal with a specific signal level and/ora specific signal frequency with the measurement system; measuring asignal level and/or a signal frequency with the calibration system atthe first output of the signal splitter, measuring a signal power at thesecond output of the signal splitter and transmitting measured values tothe first measurement unit; determining a difference between themeasured signal level and/or the measured signal frequency and thegenerated signal with the specific signal level and/or the specificsignal frequency; and calculating calibration data by using thedetermined difference between the measured signal level and/or themeasured signal frequency and the generated signal with the specificsignal level and/or the specific signal frequency.
 2. The methodaccording to claim 1, further comprising the steps of: generating asignal with a second specific signal level and/or a second specificsignal frequency with the calibration system; measuring a second signallevel and/or a second signal frequency with the measurement system;determining a difference between the measured signal level and/or themeasured signal frequency and the generated signal with the specificsignal level and/or the specific signal frequency; and calculatingsecond calibration data by using the determined difference between themeasured signal level and/or the measured signal frequency and thegenerated signal with the specific signal level and/or the specificsignal frequency.
 3. The method according to claim 1, wherein theswitch-extender further comprises at least one attenuator or the atleast one first attenuator and a second attenuator in series and forevery output port a signal connector is connected to theswitch-extender, and wherein the method further comprises the step of:adjusting the attenuation value of the at least one first attenuator oradjusting the attenuation value of the at least one first attenuator andthe second attenuator so that the measured signal level and/or signalfrequency of the signal is equal to the generated signal with thespecific signal level and/or the specific signal frequency.
 4. Themethod according to claim 3, further comprising the steps of: repeatingthe generating step, the measuring step, the determining step and thecalculating step for another signal frequency and/or signal level, orrepeating the generating step, the measuring step, the determining step,the adjusting step and the calculating step for another signal frequencyand/or signal level.
 5. The method according to claim 3, wherein asignal connector is a cable, and wherein the method further comprisesthe steps of: connecting the other end of another signal connector withanother attenuator to the calibration system; and repeating thegenerating step, the measuring step, the determining step and thecalculating step for another signal frequency and/or signal level, orrepeating the generating step, the measuring step, the determining step,the adjusting step and the calculating step for another signal frequencyand/or signal level.